February 2000 newsletter

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Beware skin bends

While some textbooks describe skin bends as a minor manifestation of decompression sickness there is increasing evidence of an association with intra-cardiac shunting. A recent case highlights the risk : A 40 year old experienced male diver had several episodes of skin irritation after diving well within recommended limits. He developed an itchy rash with obvious erythema and this persisted for up to two days. He then had a recurrence of his usual migraine headache aftertwo further dives before finally requiring recompression because of shoulder and arm pain following a dive well within recommended decompression limits. His symptoms resolved quickly with recompression and he is now asymptomatic. Subsequent investigation revealed an atrial septal defect measuring almost 1.5 cm in diameter with rapid passage of intravenous contrast from the right to left heart. This defect is due to be closed percutaneously using an Amplatzer occluder device shortly. The UKSDMC advises that divers should be investigated after even one skin bend because of the danger of subsequent neurological damage.

Ventriculo-atrial and ventriculo-peritoneal shunts

Following two recent queries the committee has clarified the advice for divers with shunts inserted for the relief of intracranial hypertension (hydrocephalus). There are two main shunt types and the risks when diving are different for each. Shunts are often inserted in early childhood although adults may also develop intracranial hypertension, particularly with posterior fossa tumours. The first condition for diving is that the shunt must either be unnecessary (and therefore occluded) with no evidence of recurrent hydrocephalus, or that the shunt is fully functional with no recent episodes of infection. There should be no detectable neurological deficit on examination.

V-P shunts should not cause a problem when diving since there is no prospect of intra-vascular bubble formation related to the shunt, and there should be little pressure differential when diving. V-A shunts are different since right atrial pressure can vary considerably during diving. Venous return is usually increased because of the removal of gravity and in some cases because of leg compression when wearing a dry suit. Ear clearing by the Valsalva technique and coughing will also increase right atrial pressure. Theoretically there is an increased risk of bubble formation at the shunt insertion point. The other risk is of shunt malfunction because of extreme pressure change. There is a risk of epilepsy following shunt insertion and divers should meet the published standards, ie being seizure free for five years following insertion without requiring anticonvulsant medication.

Exercise testing in the surgery

Some individuals require exercise testing to predict their ability to cope with the physical stress of diving. There are countless exercise protocols including the Army step test which is commonly used. The disadvantage of many of these tests is the lack of gradation and the ability to quantify exercise capacity for comparison purposes. The Chester Step Test addresses some of these points and involves stepping on and off a 10 or 12 inch step at a rate set by a metronome recorded on a cassette. This starts at 15 steps per minute and gradually increases every two minutes by 5 steps per minute. Measuring the heart rate at each stage allows prediction of maximum aerobic capacity and this is an objective measure of aerobic fitness. The test has been well validated and is easy to perform within the surgery. It does require a heart rate monitor but these are easily available and can even be bought from sports shops. The Chester Step Test was developed by Dr Kevin Sykes at the Chester College of Higher Education., Parkgate Road, Chester, CH1 4BJ.
For further background information consult: Aerobic fitness testing: an update. Stevens N, Sykes K. Journal of Occupational Health 1996;48(12):436-8.

SSRI's and diving

As mentioned in the last newsletter there are more divers than ever using antidepressants, particularly the selective serotonin reuptake inhibitors such as fluoxetine (prozac). This is thought to be dangerous when diving because of the risks of the medication, and the underlying condition. Some individuals require SSRI’s for anxiety or stress symptoms rather than clinical depression but these patterns of behaviour are not ideal personality traits for any diver who may have to cope with very dramatic events underwater.

The SSRI’s are less sedative than other antidepressants such as the tricyclics, although the recognised side effects still include drowsiness, dizziness and rarely convulsions or mania. Their effect in humans at hyperbaric pressure is largely unknown and there are no published studies in a peer reviewed journal examining this issue. Given the lack of information it is not possible to advise divers on the actual risks involved. It certainly would be possible to perform an anonymous retrospective survey of divers to assess anecdotal experience with SSRI’s but the scientific value of this is limited. There are biases inherent in this technique particularly since enthusiasts are more likely to reply to the survey, rather than those no longer involved in diving because of drug related problems. The solution may lie in performing a prospective safety audit, similar to the diabetes and diving database asking divers on SSRI’s to detail their diving pattern. An additional study would be to examine volunteers established on SSRI’s by psychometric testing at hyperbaric pressure although this would provide limited information on the effects of such drugs in the real world when diving in the cold, sometimes murky water around the UK.

It is reasonable to continue the ban on diving with other classes of psychiatric medication because of the more prevalent side effects likely to interfere with diving. The paternalistic and protectionist approach in assessing fitness to dive is often criticised but sport diving is unusual in that divers are not simply responsible for their own safety, but have to be able to provide help for their buddy in an emergency. The diver can certainly be asked to give informed consent to diving while taking SSRI’s but the buddy should also be asked to consent to their involvement. This raises confidentiality issues which are difficult to resolve.

There are two conflicting approaches to the problem. The first is to assume that SSRI’s and sport diving are incompatible and that the current ban should continue. This would be a safe approach but there would be no supporting evidence and such a policy could lead to the unnecessary exclusion of divers. The second is to assume that SSRI’s are unlikely to cause problems when diving if the individual has no examination abnormalities, has no reported side effects from their medication, and assuming that the underlying condition is well controlled and not a recognised contraindication to diving.

The committee currently recommends that any individual taking SSRI’s should be advised against diving. Exceptional cases should be referred for consensus assessment and if approved then these divers will be followed as a prospective cohort. Scientific studies are already being designed to assess the effects of SSRI’s at pressure.